Prof. Kihwan Kim’s trapped ion group at the Center of Quantum Information of the Institute for Interdisciplinary Information Sciences realized a quantum simulation of molecular vibronic spectroscopy in a trapped ion system. The work was published in Chemical Science on Jan 28th, 2018, and entitled “Quantum Optical Emulation of Molecular Vibronic Spectroscopy Using a Trapped-ion Device.”

Fig.1 A schematic diagram of a trapped ion system for simulating molecular vibronic spectroscopy

With the rapid development in the field of quantum computation, the number of qubits and the fidelity of quantum operations have been greatly improved. It is expected that in the near future a quantum computer will be able to demonstrate better performance for a certain problem that is insoluble by classical computers. Boson sampling is one of the well-defined problems that can demonstrate the outperformance of the quantum computer. Though the power of quantum computer can be revealed through boson sampling, it appears as a somewhat artificial problem that may not be related to a more worthwhile problem. Recently, it was pointed out that with modification, the boson sampling problem can be connected to molecular vibronic (vibrational+electronic) spectroscopy.

In our work, inspired by the proposed theory, we provide the experimental evidence that the sampling of the molecular vibronic spectrum can be done for the first time. Moreover, it was demonstrated with phonons in a trapped-ion system, not photons in photonic systems, which have already been attempted by many other groups. In order to perform a reliable sampling with phonons, we have developed the essential experimental technology for the phase-coherent manipulation of displacement, squeezing, and rotation with multiple motional modes in a single realization. We have also developed collective projection measurement on two phonon modes at up to 10 phonons per mode. Finally, as an example, we have obtained the photoelectron spectrum of sulfur dioxide (SO2) and observed that the results are consistent within the experimental error bars. We believe our demonstration paves the way to perform molecular sampling beyond the limits of classical computation.

Fig.2 The experimental results of simulated SO2 vibronic spectroscopy

Yangchao Shen, Yao Lu, Kuan Zhang, Junhua Zhang and Shuaining Zhang developed the experimental setup, performed the experiment, and recorded the data. In the paper, Yangchao Shen, a PhD. candidate at IIIS, is the first author. The corresponding authors are Joonsuk Huh, Assistant Professor at Sungkyunkwan University in Korea, and Kihwan Kim, Tenured Associate Professor at IIIS, Tsinghua University. The research was funded by the National Basic Research Program of China, and the National Natural Science Foundation of China.